Bitumen is a complex matrix, originating from double distillation of raw petrol and essentially composed of aromatic, naphthenic or aliphatic hydrocarbons. Highly viscous or even solid at ambient temperature, it fluidifies and drains off as a Newtonian liquid as soon as its temperature reaches one hundred degrees. The physico-chemical characterisation of bitumen is not easy: dissolution in an adapted hydrocarbon (heptane, for example), separates it into two large families which are maltenes and asphaltenes. The latter constitute the solid, polar part of very high molecular weight of bitumen, giving it a certain number of particular properties.
Due to its different properties, especially its properties of adhesion to most standard media, sealing, stability, thermal and dielectric insulation, and elasticity, bitumen is used in many fields and especially in the field of building and public works (BTP) for road surfacing and sealing membranes.
To reinforce its properties, allow for easier handling and boost its quality, researches have been conducted to modify bitumen and form a modified bitumen or a bituminous binder.
Among modifications imposed over time, incorporating polymers into bitumen has been the most significant (modified bitumen). Whether plastomers, such as polyethylene or polypropylene, or thermoplastic elastomers, such as styrene-butadiene-styrene or styrene-isoprene-styrene, these polymers give bitumen a better elasticity, especially a decrease in thermal susceptibility resulting in a better resistance to cracking at low temperatures, a greater rigidity at high temperatures, and a better resistance to fatigue.
Despite the advantages brought by incorporating polymer into bitumen, the latter cause novel problems such as the production cost of bituminous binder and the considerable sensitivity to temperature and/or ultraviolet radiation of some polymers.
Bitumen or modified bitumen can also be additivated with mineral fillers, for example limestone fillers, or silicates, which can be flame-proofing or not, with various additives in function with the preferred properties of the final product, and be reinforced by a grid comprising fibres of glass and/or polyester (in this case especially sealing membrane) to form the bituminous binder. Some membranes are covered in other mineral products such as sand, or slates, the aim of which, inter alia, is to protect the bituminous binder from ultraviolet radiation. “Soluble elements” will be mentioned hereinbelow to designate the polymers and additives, while mineral fillers and protective elements against ultraviolet rays, and different fibres will be qualified as “insoluble elements”.
All these elements tend to make bitumen-based products complex and sources of technical, economic and environmental problems as to their recycling and covering.
Several methods for recycling bituminous products are known from the prior art.
It is for example known to recycle bituminous products by solvolysis. For this, the bituminous product is mixed with a solvent adapted to dissolving bitumen so as to separate the bitumen, and if needed the soluble elements, from the insoluble elements also included in the bituminous product.
However, such a recycling method is also highly restrictive to the extent where the bitumen dissolves slowly, needing several hours, and therefore fails to ensure sufficient yield.
It is also known to recycle bituminous products via thermal processing. For this, the bituminous product is heated so as to separate the bitumen from non-meltable elements of the bituminous product such as fillers.
Also, in both these cases, it is necessary to carry out in advance crushing or cutting of the bituminous product to be recycled so as to increase its specific surface and accordingly favour the dissolution or the fusion of the bitumen. Yet, such crushing or cutting is particularly complicated to perform on the one hand given the viscosity of the bituminous binder which, when heated by the crushing operation, binds the tools and on the other hand given the insoluble elements which were able to be introduced to the bitumen to form the bituminous product, especially the fibres of glass and/or polyester forming the grid.
Also, the high temperatures required for thermal processing and the presence of solvent for solvolysis can pose problems of hygiene, safety and environment.
Another problem relating to use of recycled bituminous binder is due to ageing which the latter undergoes during its lifecycle. In fact, during recycling of bituminous products, even though the recycled bituminous binder (that is, the bitumen separated from the insoluble elements of the initial bituminous product but preserving the soluble elements of said initial bituminous product) is mixed with virgin bitumen and novel insoluble elements (mineral fillers, etc.) and/or novel soluble elements (polymers, etc.), the performance of the bituminous product obtained from this recycled bituminous binder is altered all the same.
The principal mechanism of ageing of bitumen is its oxidation. In fact, the aged bituminous binder has higher viscosity and is more rigid than its virgin version and obvious changes in its composition are observed. These changes can especially result in loss of adhesion of the bituminous product, or in its cracking.
In this respect, rejuvenating of the bituminous binder can prove to be an important part of the recycling process.
For this, it is for example known to use products for rejuvenating bitumen. These products are in general mixed with the bituminous product to be recycled to restore the original characteristics of the oxidised (aged) bitumen in order to soften it and regenerate the volatile materials and the dispersion oils while benefiting adhesion. They restore the initial rapport between asphaltenes and maltenes. Rejuvenating products must generally be strongly aromatic and be able to improve both sensitivity to temperature and hardening of the aged bitumen. They must be composed to boost the peptization power of the maltene phase.
Cooking oil or recycled engine oil, palm oil, canola oil, or sunflower oil are examples of rejuvenating products of bitumen known to the expert. Such rejuvenating products are for example described in the document by Hallizza Asli et al, Investigation on physical properties of waste cooking oil-Rejuvenated bitumen binder, Construction and Building Materials 37 (2012) 398-405 relating to the use of cooking oil as rejuvenating products.
According to the grade of the bitumen and the proportion of the added rejuvenating oil (1 to 5% of the volume of bitumen to be rejuvenated), the viscosity, the point of softening, penetrability, and flash point all vary. However, mixing the aged bitumen with the cooking oil in a proportion of 4 to 5% of the volume of bitumen can produce excellent rejuvenating results.